On the bottom floor of the submarine, there will be two rooms that must be opened by your respective timeline skill (Lockpicking or Hotwiring). On the bed in one of these rooms is the Enigma Code. Both are accessible to one another via a metal plate that can be opened with the Lazerkraftwerk.

On the bottom floor of the submarine, there will be two rooms that must be opened by your respective timeline skill (Lockpicking or Hotwiring). On the desk next to a radio will be the gold letter opener. Both are accessible to one another via a metal plate that can be opened with the Lazerkraftwerk.